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(#) Lifecycle Annotation Processor with Java 8 Compile Option

!!! WARNING: Lifecycle Annotation Processor with Java 8 Compile Option
   This is a warning.

Id
:   `LifecycleAnnotationProcessorWithJava8`
Summary
:   Lifecycle Annotation Processor with Java 8 Compile Option
Severity
:   Warning
Category
:   Performance
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   3.5.0 (August 2019)
Affects
:   Gradle build files
Editing
:   This check runs on the fly in the IDE editor
See
:   https://d.android.com/r/studio-ui/lifecycle-release-notes
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/GradleDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GradleDetectorTest.kt)

For faster incremental build, switch to the Lifecycle Java 8 API with
these steps:

First replace
```gradle
annotationProcessor "androidx.lifecycle:lifecycle-compiler:*version*"
kapt "androidx.lifecycle:lifecycle-compiler:*version*"
```
with
```gradle
implementation "androidx.lifecycle:lifecycle-common-java8:*version*"
```
Then remove any `OnLifecycleEvent` annotations from `Observer` classes
and make them implement the `DefaultLifecycleObserver` interface.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
build.gradle:3:Warning: Use the Lifecycle Java 8 API provided by the
lifecycle-common library instead of Lifecycle annotations for faster
incremental build. [LifecycleAnnotationProcessorWithJava8]
  annotationProcessor "android.arch.lifecycle:compiler:1.1.1"
                      ---------------------------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`build.gradle`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~groovy linenumbers
dependencies {
  implementation "android.arch.lifecycle:runtime:1.1.1"
  annotationProcessor "android.arch.lifecycle:compiler:1.1.1"
}android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GradleDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `GradleDetector.testJava8WithLifecycleAnnotationProcessor`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection LifecycleAnnotationProcessorWithJava8
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="LifecycleAnnotationProcessorWithJava8" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'LifecycleAnnotationProcessorWithJava8'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore LifecycleAnnotationProcessorWithJava8 ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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